1. Field of the Invention
This invention relates to a hydraulic clutch of the multi-disc type for use in a motorcycle or the like.
2. Prior Art
One conventional hydraulic clutch 10 as disclosed in Japanese Patent Application Laid-Open (Kokai) No. 59-200818 comprises an annular drive member 12 attached to an input gear 14 rotatably mounted on a hollow output shaft 16, an annular driven member 18 fixedly mounted on the output shaft 16 for rotation therewith, an annular clutch pressure member 20 mounted on a central boss 18a of the driven member 18 for axial sliding movement and having a tubular portion 20a, and a clutch piston 22 mounted on the output shaft 16 and received in the tubular portion 20a of the clutch pressure member 20 held in sliding contact therewith at an outer periphery thereof. A plurality of drive friction discs or plates 24 are mounted on the drive member 12 for axial sliding movement while a plurality of driven friction discs or plates 26 are mounted on the driven member 18 for axial sliding movement, the drive and driven discs 24 and 26 being disposed alternately in closely spaced relation and being prevented from rotation relative to the drive and driven members 12 and 18, respectively. An annular hydraulic pressure chamber 28 for holding a pressurized fluid or oil is defined by the boss 18a of the driven member 18, the clutch piston 22 and the clutch pressure member 20. A clutch lifter plate 30 is secured to the clutch pressure member 20 through a bushing 32 and a bolt 34 in such a manner that the clutch lifter plate 30 is movable relative to the clutch pressure member 20 a distance h. An annular clutch spring 36 is interposed between the driven member 18 and the clutch lifter plate 30 to normally urge the clutch lifter plate 30 in a direction away from the driven member 18. The clutch pressure member 20 has a pressure-receiving wall 20b and a bore 20c in which a valve actuator pin 38 is received for axial movement, the valve actuator pin 38 having a rear end secured to the clutch lifter plate 30 while a front end of a reduced diameter is slidably fitted in an aperture 40 formed through the pressure-receiving wall 20b of the clutch pressure member 20. A valve outlet port 42 is formed through the pressure-receiving wall 20b for communicating the pressure chamber 28 with the bore 20c. A valve element 44 in the form of a reed is secured to the pressure-receiving wall 20b at one end thereof for closing the outlet port 42. The front end of the valve actuator pin 38 is spaced from the valve element 44 by a distance slightly less than the distance h. The valve element 44, the valve actuator pin 38 and the pressure-receiving wall 20b having the valve outlet port 42 constitute a hydraulic pressure control valve for controlling the operation of the clutch 10. Oil under pressure is fed from a source of pressurized oil to the pressure chamber 28 via a feed pipe 46 within the hollow shaft 16 and an inlet port 48 formed through the peripheral wall of the shaft 16. A lifter piece 50 is slidably received in the end of the hollow shaft 16, and a flange 50a of the lifter piece 50 is engaged with the clutch lifter plate 30 through a bearing 52. A cam shaft 54 has a cam surface 54a with which an outer end of the lifter piece 50 extending outwardly of the shaft 16 is engaged.
When the clutch 10 is in its engaged condition, the clutch lifter plate 30 is held away from the driven member 18 under the influence of the clutch spring 36 with the valve element 44 closing the outlet port 42. Therefore, the pressure in the hydraulic pressure chamber 44 is kept to a sufficient level to urge the clutch pressure member 20 toward the driven member 18 to hold the drive and driven friction discs 24 and 26 in firm engagement. Thus, the rotation of the input gear 14 driven for rotation by a drive gear (not shown) is transmitted to the output shaft 16 via the drive member 12, the drive and driven friction discs 24 and 26 and the driven member 28. For disengaging the clutch 10, the cam shaft 54 is rotated to move the lifter piece 50 inwardly through the cam surface 54a, so that the clutch lifter plate 30 is also moved inwardly against the bias of the clutch spring 36. In this case, the clutch lifter plate 30 is first moved a distance h, so that the front end of the control pin 38 urges the valve element 44 away from the pressure-receiving wall 20b of the clutch pressure member 20 to open the outlet port 42. As a result, the pressurized oil in the pressure chamber 28 is caused to flow through the outlet port 42, the bore 20c and a port 56 to reduce the pressure in the pressure chamber 28. In this condition, the drive and driven friction discs 24 and 26 are held together only under the force of the clutch spring 36. Upon opening of the outlet port 42, a control coil spring 58 acting between the clutch pressure member 20 and the clutch lifter plate 30 serves to keep them apart from each other a predetermined distance. This ensures that the engagement of the clutch 10 is started properly and that viscous drag occurring between the drive and driven friction discs 24 and 26 due to the presence of oil is positively prevented. A further rotation of the cam shaft 54 brings the clutch lifter plate 30 into engagement with the clutch pressure member 20 to move it toward the drive member 12, thereby bringing the drive friction discs 24 completely out of engagement with the driven friction discs 26.
Thus, with this conventional clutch 10, since the valve actuator pin 38 is first to be moved a distance h to open the outlet port 42 to reduce the pressure in the pressure chamber 28, the valve actuator pin 38 and those component parts operatively associated therewith must be set accurately in proper positions when assembling the clutch 10, and they must have great dimensional accuracy. In addition, the control spring 58 must be adjusted to a predetermined load. Therefore, the manufacturing cost of the clutch 10 as well as its maintenance cost is rather high.